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[x86] inline calls to fmaxf / llvm.maxnum.f32 using maxss (PR24475)

Description

[x86] inline calls to fmaxf / llvm.maxnum.f32 using maxss (PR24475)

This patch improves on the suggested codegen from PR24475:
https://llvm.org/bugs/show_bug.cgi?id=24475

but only for the fmaxf() case to start, so we can sort out any bugs before
extending to fmin, f64, and vectors.

The fmax / maxnum definitions provide us flexibility for signed zeros, so the
only thing we have to worry about in this replacement sequence is NaN handling.

Note 1: It may be better to implement this as lowerFMAXNUM(), but that exposes
a problem: SelectionDAGBuilder::visitSelect() transforms compare/select
instructions into FMAXNUM nodes if we declare FMAXNUM legal or custom. Perhaps
that should be checking for NaN inputs or global unsafe-math before transforming?
As it stands, that bypasses a big set of optimizations that the x86 backend
already has in PerformSELECTCombine().

Note 2: The v2f32 test reveals another bug; the vector is extended to v4f32, so
we have completely unnecessary operations happening on undef elements of the
vector.

Differential Revision: http://reviews.llvm.org/D15294

Details

Committed
spatelDec 15 2015, 3:11 PM
Differential Revision
D15294: [x86] inline calls to fmaxf / llvm.maxnum.f32 using maxss (PR24475)
Parents
rL255699: Removing files that I didn't mean to checkin.
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